(Invited) Towards Addressing Fundamental Scale-up Questions for Low-Temperature Electrolysis Electrodes

Abstract

Industry and government aspirations continue to converge regarding the need for energy-system-wide solutions to environmental, sustainability, and climate challenges. Among other bold programs, the Department of Energy’s Hydrogen-at-Scale initiative seeks to exploit the most abundant element on the planet as a ubiquitous energy source, touching nearly every aspect of the energy, industrial, and transportation systems as a long-term storage medium, a feedstock, a processing agent, or a fuel. Central to the concept is the ability to generate hydrogen from water by leveraging clean and low-cost electricity from renewables. Low-temperature water electrolysis (LTE) systems are seen as the primary engine for clean hydrogen generation and are envisioned to provide a pathway to gigawatt-scale production. At present, however, volumes for LTE system are still small, and thus high-volume manufacturing of the electrochemical cell materials, as well as stack and system components, is also aspirational. The membrane electrode assembly (MEA) is where the rubber meets the road for these systems, in terms of performance and lifetime, and account (depending on production volume) for approximately half of system costs. Membranes for the LTE MEAs are commercially available, though further improvements in cost, performance, and durability are still rightly sought. Electrodes on the other hand, are at present a bit of a black box. Further development of catalysts and ion-conducting polymers notwithstanding, fundamental questions about electrode structure and fabrication remain to be answered. What is their optimal morphology (and is it the same for performance and durability)? How do the formulation, properties, and processing of the dispersed catalyst-ionomer ink impact the morphology? How do the physics and parameters of the coating and drying processes also impact the morphology? Research efforts to address these questions are complicated by multiple pathways to construct the MEA – including decal-transfer, directly coating the membrane, or directly coating the porous media – as well as a great variety of coating processes that could be used. These different factors not only potentially affect the performance of the MEA, but they affect cost. In this talk, manufacturing pathways and challenges for LTE electrodes – informed by the greater breadth and maturity of similar work for low-temperature fuel cells – will be discussed. Along the way, examples of activities at the National Renewable Energy Laboratory and partner labs to address some of these fundamental questions, via several lab consortia and industry partnerships, will be given.